1. Technical Field
The embodiments herein generally relate to medical devices, and, more particularly, to a spinal flexion and extension motion damper used during orthopedic surgeries.
2. Description of the Related Art
Patients who have a lumbar spinal fusion have an increased risk of having adjacent segment disease. Adjacent segment disease occurs after the spinal fusion in which the segment or the intervertebral disc and the facet joints are degenerated at the adjacent level above (and sometimes below) the lumbar fusion. This disease can produce severe pain that can affect the spinal cord's ability to properly function. Often, a disorder in one spinal component can lead to ultimate disorder, and finally pain in another component. These can also lead to spinal stenosis in which the spinal canal narrows and compresses the spinal cord and nerves. Laminectomy is a surgical procedure which is used for treating spinal stenosis by relieving pressure on the spinal cord. In this procedure, a part of the lamina (e.g., a part of the vertebra) is removed or trimmed to widen the spinal canal and create more space for the spinal nerves.
One way of accomplishing spinal fusion involves the use of devices such as a series of pedicle screw assemblies and connecting rods. Generally two pedicle screws are placed per vertebra and screwed into the pedicles. They include receiver elements for accommodating the connecting rods. Clamping elements are also adapted for receiving and joining the connecting rod to the screws. The spinal fusion using pedicle screw assemblies can be strengthened by attaching a spinal cross-connector between the connecting rods. Spinal cross-connectors are often used to provide additional stability to the devices. When the connecting rods are fastened in parallel on either side of the lamina, the pedicle screw assembly can be significantly strengthened by using a cross-connector to bridge the connecting rods. The cross-connectors are usually in the form of a rod having a clamp on each end for connecting with the connecting rods.
It is observed that more rigid spinal fixation systems may increase the risk of complications such as mechanical failure, adjacent segment disease, and device-related osteoporosis. To avoid these complications and concurrently obtain adequate immobilization, it is important to stabilize the affected mobile vertebral segment while controlling its degree of flexion and/or extension motion. Control of abnormal motions may relieve pain and prevent adjacent segment degeneration. Thus, an ideal spinal fixation system should provide dynamic stabilization as well as preservation of motion.
Traditional pedicle screw assemblies include a rubber bungee within a plastic tube placed between the heads of two pedicle screws. It provides dynamic stabilization to the motion segment, but typically requires extensive muscle dissection to place, and generally cannot work as an adjacent segment protector above a pedicle screw instrumented fusion. Another example is a solid device generally made up of titanium that is placed between two laminas to widen the inter-spinous and interlaminar space and to limit extension of the motion segment. In this way it is designed to relieve the symptoms of spinal stenosis but typically cannot work when a laminectomy has been performed. Furthermore, it generally has no ability to limit flexion, and is very rigid. Moreover, it typically cannot work to protect against adjacent segment disease. Also, these generally lack a limitation of the damping ability, which may lead to damage of the vertebrae during natural motion. Generally, there are no other known systems that stabilize the spine either rigidly or dynamically by utilizing the spinous process with a pedicle screw fixation assembly (regardless of the presence of an optional cross connector). Accordingly, there remains a need for a new damper system to control the degree of flexion and/or extension motion of the mobile vertebral segment while providing additional stability to the spine.